The present invention relates to a shaft sealing structure applicable to a rotation shaft of a large fluid machine such as various kinds of turbines, compressors, water turbines or wheels, refrigerating machines, and pumps, and in particular, to a gas or steam turbine to which a shaft seal is applied.
A typical gas turbine generates power by introducing a high-temperature and high-pressure gas into a turbine so as to expand the gas, and converting the thermal energy of the gas into mechanical rotational energy. Such a gas turbine has a seal mechanism (i.e., shaft seal), arranged between stationary blades and -the rotation shaft, for reducing the leakage of the combustion gas, that is, the amount of gas which leaks from the high-pressure side to the low-pressure side. Conventionally, a non-contact labyrinth seal is widely known and used as such a sealing structure. When the labyrinth seal is employed, it is necessary to have a relatively large gap at the end of each fin so as to prevent the fin from contacting the face which faces the fin even if the shaft is vibrated during a transitional period of the rotation, or if the relevant portion is thermally and transitionally deformed. Therefore, the leakage is relatively large in the labyrinth seal. As a substitute for the labyrinth seal, a brush seal has been developed so as to reduce the leakage.
FIGS. 37A and 37B show a general structure of the brush seal. In the figures, reference numeral 1 indicates a rotation shaft, reference numeral 2 indicates a casing, reference numeral 3 indicates a low-pressure side end plate, reference numeral 4 indicates a high-pressure side end plate, reference numeral 5 indicates a brazed portion, and reference numeral 6 indicates a wire bundle. The wire bundle 6, having a width of 1 to 3 mm, consists of filaments closely arranged with no gap between each other, and each filament has a diameter of 50 to 100 xcexcm and suitable rigidity by which eccentricity due to vibration or thermal deformation of the rotation shaft 1 or the like can be absorbed. In addition, the wire bundle 6 is inclined with respect to the rotation direction so as to make an acute angle between the wire bundle and the outer-peripheral surface of the rotation shaft 1. The end of the wire bundle 6 contacts the outer-peripheral surface of the rotation shaft 1 via a specific pre-load, thereby reducing the leakage in the axial direction of the shaft.
The wire bundle 6 slides on the rotation shaft 1 in contact with the shaft. This sliding motion may heat the wire bundle 6 and make the bundle red, according to the environmental conditions or the rotation speed. Therefore, the wire bundle 6 may be made of a heat-resisting material such as inconel or hastelloy according to the usage condition. In addition, the sliding surface, that is, the outer-peripheral surface of the rotation shaft 1, is also subject to abrasion, as in the wire bundle 6; thus, the relevant surface of the rotation shaft 1 is coated with an abrasion resistant material. Furthermore, the wire bundle 6 has smaller rigidity in the axial direction of the rotation shaft 1; thus, the inner diameter of the low-pressure side end plate is made approximately the same as the diameter of the circumference of the rotation shaft 1, thereby preventing breakage of the wire bundle 6.
The above brush seal has the following problems.
In the brush seal, leakage through gaps between the wires of the bundle 6 or gaps near the end of the bundle, or around the sliding portion (i.e., face) contacting the outer-peripheral surface of the rotation shaft 1 is a typical problem. If the differential pressure of the seal exceeds a permissible value which is determined based on the diameter of each wire of bundle 6, the structure or arrangement of the low-pressure side end plate, and the like, the wire bundle 6 is deformed towards the low-pressure side, so that the area between the wire bundle 6 and the rotation shaft 1 is not sealed and thus the sealing effect cannot be obtained.
The rigidity of the wire bundle 6 as a constituent of the brush seal is determined according to the following capability of the wire bundle 6 with respect to the vibration of the rotation shaft 1, or to a suitable pre-load between the wire bundle 6 and the rotation shaft 1. The rigidity can be increased by using a thicker wire, but this has limits. That is, the maximum differential pressure for sealing in the axial direction of the rotation shaft 1, dependent on the rigidity of wire bundle 6, is approximately 5 kgf/cm2, and a much larger differential pressure cannot be maintained using a seal. Generally, the diameter of each wire is approximately 50 to 100 xcexcm, that is, very thin. Therefore, when such thin wires contact and slide on the peripheral surface of the rotation shaft 1, the wire bundle 6 may be broken and come off, and this is a serious problem when the relevant gas turbine is operated for a long time.
The leakage around the end portion of the wire bundle 6 is much smaller than that of the labyrinth seal or the like, because the wire bundle 6 contacts the peripheral surface of the rotation shaft 1 when it slides on the surface. However, it is difficult to reliably maintain a smaller leakage between the wires of the wire bundle 6.
In addition, the peripheral surface of the rotation shaft 1 must be coated with an abrasion resistant material because the wire bundle 6 and the peripheral surface contact each other during the sliding motion. However, a technique for making an anti-abrasion coating C which suits a rotation shaft having a large diameter and lasts for a long time has not yet been established, and the wire bundle 6 and rotation shaft 1 suffer considerable abrasion. Therefore, the brush seal has a short lifetime and must be frequently replaced.
It is an object of the present invention to provide a shaft seal which has a high sealing capability and by which leakage can be reduced. Another object of the present invention is to provide a turbine using the above shaft seal, in particular, a gas turbine which has a high abrasion resistance in the seal structure, and can reduce the gas leakage from the high-pressure side to the low-pressure side.
Therefore, the present invention provides a shaft seal having flexible leafs (i.e.,) which are multi-layered to form a ring shape. Typically, one side of the multi-layered leaves is fixed to a fixing member having a cylindrical shape, and the shaft seal is arranged around a predetermined shaft (mainly, a rotation shaft).
According to the leaves employed as a sealing component, the area fixed to the casing is larger in comparison with the conventional wires; thus, the leaves are firmly fixed to the casing, thereby preventing the leaves from falling off from the casing, as observed in the conventional brush seal.
In addition, the top ends of the leaves have flexibility in the circumferential direction of the rotation shaft, and have high rigidity in the axial direction of the rotation shaft. Therefore, the leaves are not easily deformed in the direction of the differential pressure; and thus the permissible value of the differential pressure to be sealed can be increased.
When the vibration of the rotation shaft is large near the resonance point or the like, the leaves are deformed and the contact state with the rotation shaft is eased. In addition, under the rated conditions, the ends of the leaves separate from the surface of the shaft due to the dynamic pressure generated by the rotation of the rotation shaft. Therefore, it is possible to prevent excessive heating and abrasion caused by the contact of the leaves and the rotation shaft. Furthermore, according to the prevention of the heating due to the contact between the leaves and the rotation shaft, vibration generated depending on the thermal balance in the rotation shaft can also be prevented.
In the above structure, each leaf may be inclined with respect to the radial direction of the shaft. In particular, if each leaf is inclined with respect to the radial direction of the shaft in a manner such that each leaf leans towards the opposite direction of the rotation direction of the rotation shaft, then the top ends of the leaves are separated from the surface of the rotation shaft due to the dynamic pressure generated by the rotation of the rotation shaft. Therefore, contact between the rotation shaft and the leaves is prevented.
In this case, if each leaf has a flat plate shape, and is inclined with respect to the peripheral surface of the rotation shaft by 30 to 45 degrees, then the flexural rigidity of the plate is small and the top ends of the leaves are separated from the surface of the rotation shaft due to the dynamic pressure generated by the rotation of the shaft. Therefore, the resistance in the rotation direction also becomes smaller, thereby reducing the sealing loss of the shaft seal.
The gap between adjacent leaves can be substantially the same at both the inner-peripheral side and the outer-peripheral side of the ring-shaped shaft seal. In this case, it is possible to much more closely arrange the leaves, and to make the gap between the rotation shaft and the top ends of the leaves much smaller in comparison with the conventional non-contact labyrinth seal. Accordingly, it is possible to remarkably reduce the leakage of the gas, and as a result, the performance of the (gas) turbine can be improved.
Here, if the seal diameter is sufficiently large (for example, approximately 1000 mm), then the gaps between the leaves can be significantly the same. However, if the seal diameter is relatively small, uniformly-curved leaves, which have a circular-arc shape (that is, the curvature gradually changes in the radial direction), are preferably used so as to make the widths of the gaps (between the leaves) substantially the same. Therefore, also in this case, it is possible to much more closely arrange the leaves, and the leakage through the gaps between the leaves can be reduced, thereby improving the efficiency of the turbine employing the present shaft seal.
Also in the shaft seal of the present invention, buoyancy providing means may be provided at the shaft-side top end of each leaf. If the shaft seal employing this structure is applied to the rotation shaft of a turbine, then during the rated operation, the top ends of the leaves are efficiently separated from the rotation shaft due to the dynamic pressure, thereby effectively preventing the contact between the rotation shaft and the leaves.
As a preferable example, the buoyancy providing means is a slope wherein the distance between the top point of the leaf and the peripheral surface of the rotation shaft (around which the shaft seal is arranged) gradually decreases along the rotation direction of the shaft. In this case, a dynamic pressure is caused by the wedge effect of the slope, so that the top ends of the leaves are separated from the rotation shaft.
Such a slope can be formed by the following processing method comprising the steps of:
(1) fixing the outer-peripheral base ends of the leaves in a manner such that each leaf is inclined with respect to the radial direction of the shaft and that each leaf leans towards the opposite direction of the rotation direction of the rotation shaft;
(2) pushing the inner-peripheral free ends of each leaf in a manner such that the acute angle between the leaf and the peripheral surface of the rotation shaft is decreased; and processing the top end of the leaf under the above pushed state, so as to make the top end substantially in parallel with the rotation shaft; and
(3) releasing the pushed state after the processing process.
As another example, the buoyancy providing means may be provided by forming a step in the end face of the top end of the leaf and in the axial direction of the shaft. In this case, buoyancy is generated due to the differential pressure at the step, so that the top ends of the leaves are separated from the rotation shaft.
As a further example, the buoyancy providing means may be provided by forming a step in the end face of the top end of the leaf and in the circumferential direction of the shaft. In this case, the top ends of the leaves are separated from the rotation shaft by using the dynamic pressure caused by the rotation.
It is possible that the direction of the width of each leaf is not parallel with the axial direction of the shaft. In this case, the length of the passage between adjacent leaves is longer than the length of the axial direction, thereby increasing the resistance of the passage. Accordingly, the leakage between the leaves can be further reduced.
Typically, when the leaves receive pressure from the high-pressure side, the top ends of the leaves are separated from the shaft. Therefore, the top ends of the leaves can be separated from the rotation shaft, and the contact between the rotation shaft and the leaves can be prevented. Accordingly, it is possible to prevent excessive heating and abrasion caused by the contact of the leaves and the rotation shaft.
Also in the shaft seal of the present invention, circumferential end plates may be respectively arranged at both sides of the leaves, and a gap may be provided between the leaves and each end plate wherein the width of the gap is as narrow as possible for the leaves to move. Accordingly, the pressure applied to the leaves from the high-pressure side and the suction force applied to the leaves from the low-pressure side are reduced, so that deformation of the leaves towards the direction of the differential pressure can be prevented and the resistance of the passage can be increased around the leaves.
Here, each leaf may be inclined with respect to the radial direction of a predetermined shaft; and the gap between the shaft and the top end of one of the end plates may be the same as the gap between the shaft and the top end of the other end plate. Accordingly, the above gap can be as small as possible for the rotation shaft to rotate, and the length of each end plate in the radial direction of the rotation shaft can be approximately the same as the length of the leaves in the radial direction, thereby much further increasing the resistance of the passage around the leaves.
In addition, the gap between one of the end plates and the leaves can be the same as the gap between the other end plate and the leaves. In this case, deformation of the leaves along the direction of the differential pressure can be much more reliably prevented.
In a variation, the outer-peripheral base end of the ring-shape leaves are attached to a circular body consisting of a plurality of separate circular-arc portions, and a division face between the separate circular-arc portions engaging each other has a step in the circumferential direction. According to this structure, the high-pressure combustion gas which reaches the junction between the separate portions cannot pass through the junction because the division face having a step blocks the gas. Therefore, it is possible to prevent the leakage of the combustion gas through the junction. In addition, the above engagement in the division face can reinforce the junction.
In another variation, the leaves are grouped into a plurality of unit segments, each unit segment including a predetermined number of leaves, and space is provided between adjacent unit segments. In this case, when the top ends of the leaves 18 separate from a contact surface, the leaves belonging to a unit segment are not much affected by the leaves belonging to adjacent unit segments because there is a space between the unit segments. Therefore, the leaves can much more easily separate from a contact surface, typically, from a rotation shaft.
It is also possible that each leaf is inclined with respect to the radial direction of the rotation shaft; and a fluid delivery unit for delivering fluid around the peripheral surface of the rotation shaft to each leaf by using the centrifugal force of the shaft is provided in an area of the rotation shaft, where leaves slides. According to this structure, the fluid around the rotation shaft is delivered toward each leaf by the centrifugal force of the shaft. Therefore, according to the pressure of the fluid, the top ends of the leaves can easily separate from the shaft, and it is possible to much more reliably prevent excessive heating and abrasion due to the contact between the rotation shaft and the leaves.
In another variation, each leaf has a gap making portion which protrudes from the surface of the leaf. If the protrusion height is the same as the width of a desired gap between the leaves, micro-gaps having a specific width can be reliably provided at both the inner-peripheral side and the outer-peripheral side, only by making the leaves contact each other via the gap making portion.
The gap making portion may be a protruding portion produced by deforming a part of the leaf. In this case, it is unnecessary to attach a separate component to the leaf; thus, the number of necessary components is not increased. Such a protruding portion can be produced by, for example, the precise pressing method.
The gap making portion may be a coated layer formed on a part of the leaf. The coated layer can be produced by using, for example, the hot dipping method. Also in this case, the gap making portion can be provided on the leaf without increasing the number of necessary components. In particular, if the coated layer is a plated layer, the thickness thereof can be determined to micrometer order, thereby precisely providing the gap (between the leaves) over the relevant circumference of the rotation shaft.
When the number of necessary components is not increased as described above, the productivity can be improved and no strict production control is necessary, thereby reducing the manufacturing cost.
In a further variation, the gap making portion is a step produced by etching a part of the leaf. That is, when a part of each leaf is etched, a step functioning as the gap making portion is formed between the etched and non-etched areas. Accordingly, the gap between the leaves can be precisely provided.
That is, only by making the leaves contact each other via the gap making portion, micro-gaps having a specific width can be reliably provided at both the inner-peripheral side and the outer-peripheral side; therefore, a turbine comprising a shaft seal structure having a high sealing capability can be easily realized.
The shaft seal may have a plurality of escape passages in the circumferential direction, wherein the escape passages are provided by making gaps between the relevant leaves have a larger width in comparison with the other gaps between the leaves.
Preferably, the escape passage is provided in some suitable leaves of the shaft seal in the circumferential direction, and is produced by removing a freely-bending portion (at the top-end side) of the target leaves (only one end of which is fixed and supported) so that in the circumferential direction, the widths of the relevant gaps (i.e., the escape passages) generated by this removing process are larger than the other gaps.
According to the above structure, a part of the pressure of the high-pressure side of the shaft seal is released to the low-pressure side through the escape passages provided along the circumferential direction of the shaft seal. Therefore, an increase of the differential pressure between the high-pressure and low-pressure sides is prevented and thus damage to the leaves due to the increase of the differential pressure can be prevented. Accordingly, even when the leaves having a smaller rigidity are used so as to improve the fluid sealing capability, no damage occurs because the above pressure-releasing function using the escape passages is effective.
It is also possible that the leaves are grouped into a plurality of unit segments, each unit segment including a predetermined number of leaves, and the leaves of each unit segment are attached to a main leaf whose thickness is larger than that of each leaf.
In a preferable example, a unit segment includes 50 to 100 leaves, and the main leaf comprises a leaf portion which is positioned between the segments and whose (outer-peripheral side) base end is brazed and fixed to the base-end side of the leaves, and a skirt portion integrally connected with the inner-peripheral side of the leaf portion, wherein a small gap is provided between the skirt portion and the outer-peripheral surface of the rotation shaft.
According to this structure, a plurality of leaves is supported as a single block by using the main leaf, so that the rigidity of the leaves can be improved. Therefore, even when the differential pressure between the high-pressure and low-pressure sides is large, the sealing of fluid can be realized using the leaves without damage. In addition, if a torsional load acts on the leaves due to the differential pressure, damage to the leaves can be prevented because of the above-explained increase of the rigidity (according to the blocked structure), thereby improving the durability.
In addition, under the rated operational conditions, the inner-peripheral side of the skirt portion of the main leaf and the outer-peripheral surface of the rotation shaft can be in a non-contact state by using the differential pressure and dynamic pressure.
If necessary, a plurality of the above-explained shaft seals are arranged around a predetermined shaft, via a spacing between each other along the axial direction of the shaft.
In this case, the pressure of the fluid in the high-pressure chamber is gradually reduced through a plurality of stages (of each shaft seal) along the axial direction of a rotation shaft or the like, and finally reaches the pressure of the low-pressure chamber when the fluid flows out from the last-stage shaft seal. Accordingly, in comparison with a structure employing a single shaft seal, the leakage of fluid can be remarkably reduced. The present invention can be effectively and easily applied to sealing of a large differential pressure around a shaft having a large diameter.
It is possible that among the shaft seals, the width in the axial direction of the shaft seal closest to the high-pressure side is largest, while the width in the axial direction of the shaft seal closest to the low-pressure side is smallest. Preferably, the pressure gradually decreases from the high-pressure side to the low-pressure side.
Here, the width L in the axial direction of each shaft seal can be defined by the following formula:
L=k(P12xe2x88x92P22)/Gxe2x80x83xe2x80x83(1)
where P1 indicates the pressure at the high-pressure side, P2 indicates the pressure at the low-pressure side, G indicates the weight flow of leakage of fluid, and k is a specific coefficient.
The weight flow of leakage G at each stage can be defied as follows:
Gxe2x88x9d(p12xe2x88x92P22)/Lxe2x80x83xe2x80x83(2)
That is, leakage G at each stage is in inverse proportion to width L in the axial direction, and in proportion to the difference of the pressures squared. Accordingly, leakage G is decreased as width L in the axial direction becomes larger.
Therefore, it is possible to determine the number of stages of the shaft seals and each width L in the axial direction by using the above formula (1) so as to realize the condition that width L1 (in the axial direction) at the high-pressure chamber (having pressure P0) side is largest, and the above L gradually decreases according to the decrease of the pressure towards the low-pressure chamber (having pressure Pa) side, and the pressure at the exit of the last stage is Pa (generally, the atmospheric pressure) of the low-pressure chamber. Under this condition, a minimum leakage of fluid from the high-pressure chamber to the low-pressure chamber can be realized. Therefore, the number of stages of the shaft seals and each width (in the axial direction) necessary for realizing the minimum leakage of the fluid can be easily determined.
The above-explained shaft seal according to the present invention is preferably applied to a gas turbine in which a high-temperature and high-pressure gas is introduced into a casing, and the high-temperature and high-pressure gas is blasted against moving blades fixed to a rotation shaft which is rotatably supported in the casing, so that the thermal energy of the gas is converted into the mechanical rotational energy and power is generated, and the shaft seal is arranged so as to seal the outer-peripheral side of the rotation shaft of the gas turbine.
Typically, the gas turbine comprises moving blades and stationary blades alternately arranged from a high-pressure stage to a low-pressure stage along the turbine shaft; and the shaft seal is arranged between the rotation shaft and one or more stationary blades.
The shaft seal may be fixed to the top end of the stationary blade. Preferably, the shaft seal is provided at least between the stationary blade of the most high-pressure side and the rotation shaft.
More specifically, the turbine comprises a casing, a compressor, a rotation shaft, moving blades attached to the rotation shaft, and stationary blades attached to the casing in a manner such that the stationary blades face the moving blades, wherein:
the shaft seals are provided between a plurality of stationary blades and the rotation shaft wherein the leaves of each shaft seal contact the rotation shaft;
under the rated operating conditions, the top ends of the leaves slightly separate from the surface of the rotation shaft due to the dynamic pressure generated by the rotation of the rotation shaft; and
when the turbine is not operated, the top ends of the leaves contact the rotation shaft again due to the elastic restoring force of the leaves.
According to this structure, the above-described effects can be obtained.
The present invention also provides a remodeling method comprising a step of exchanging an existing shaft seal (in particular, a conventional labyrinth or brush seal) arranged around a shaft of a turbine for a shaft seal according to the present invention.